Widespread temporal niche partitioning in an adaptive radiation of cichlid fishes

The partitioning of ecological niches is a fundamental component of
species diversification in adaptive radiations. However, it is presently
unknown if and how such bursts of organismal diversity are influenced by
temporal niche partitioning, wherein species avoid competition by being
active during different time windows. Here, we address this question
through profiling temporal activity patterns in the exceptionally diverse
fauna of cichlid fishes from African Lake Tanganyika. By integrating
week-long longitudinal behavioural recordings of over 500 individuals from
60 species with eco-morphological and genomic information, we provide two
lines of evidence that temporal niche partitioning facilitated this
massive adaptive radiation. First, Tanganyikan cichlids exhibit all known
circadian temporal activity patterns (diurnal, nocturnal, crepuscular, and
cathemeral) and display substantial inter-specific variation in daily
amounts of locomotion. Second, many species with similar habitat and diet
niches occupy distinct temporal niches. Moreover, our results suggest that
shifts between diurnal and nocturnal activity patterns are facilitated by
a crepuscular intermediate state. In addition, genome-wide association
studies indicate that the genetics underlying activity patterns is
complex, with different clades associated with different combinations of
variants. The identified variants were not associated with core circadian
clock genes but with genes implicated in synapse function. These
observations indicate that temporal niche partitioning contributed to
adaptive radiation in cichlids and that many genes are associated with the
diversity and evolution of temporal activity patterns. These data
are the 10fps speed and x,y position tracks for 6 days for individuals for
each of the 60 species. The behavioural analysis mostly used the 30-minute
binned data available in the supplement of the published paper.